Tag: fiber optic cable

A Concise Selection Guide for In-Line Polarizers

How do I select the right in-line polarizers? If you also have the same question in mind, then this guide will help you learn all those things that you should know for choosing the best in-line polarizers for your applications. But why do you need to buy only the best in-line polarizers? Why does their quality matter?

In-line polarizers are the small and compact fiber optic devices placed in line to improve and enhance the extinction characteristics of a fiber optic cable. They are designed to allow only one pre-defined polarization state and block the transmission of all other polarization states. Their use in many industries has become vital because if polarization extinction degrades in the fiber, it can lead to significant noise interference and reduce the performance of the entire fiber optic system.

Thus, one should never cut corners when buying in-line polarizers and should choose only the highest quality. So, without any delay, let’s find out how to buy the best in-line polarizers.

Things to Consider When Choosing the Best In-Line Polarizers

  • Polarization

It is no secret that light waves are highly susceptible to noise and interference, which is very harmful to the fiber optic systems’ performance and quality. Thus, to avoid unwanted interference and improve the performance of signals, in-line polarizers that have better control on the transfer of desired polarization state and block unwanted polarization states are considered the best choice. In short, it must transmit only linearly polarized light with a high extinction ratio and low insertion loss.

  • Signal Characteristics

The next thing you need to keep in mind includes signal characteristics. All fiber optic systems transmit light waves characterized by wavelength. Besides, a light signal is also characterized by the optical power of the signal, which is measured in dBm or mW. Due to the nature of the transport medium (i.e. fiber), fiber optic systems transmit usually longer light waves from red (650nm) to the infrared region. That’s why you see 650 nm in-line polarizers, 980nm in-line polarizers, etc. on the market.

Shorter wavelengths get perturbed due to scattering of the light source, and absorption bands at certain frequencies further attenuate the signal. Therefore, long wavelengths work better for fiber optic systems.

  • Optical Power

Optical power is the measure of wavelength and photon density. Usually, low-power signals are used in fiber optic systems. The most common units used for optical power are dBm or mW (milliwatts). A power level of 0 dBm is equivalent to 1mW, -10 dBm is 0.1 mW, and +10 dBm is equivalent to 10 mW.

  • Preferred Cable Type

In fiber optics, there are two cable types: single mode optical fiber and multimode optical fiber. While single-mode fiber cable allows a single path for light, multimode fiber cable offers multiple paths for light. It is important to note that multimode fiber cables limit the distance that a signal can travel as multiple paths of transmission force the different modes of light to disperse, and hence, they also limit transmission bandwidth. On the other hand, single-mode fiber cables facilitate signal transmission at very high bandwidth and long transmission distances.

If you need high-quality 980nm in-line polarizers or in-line polarizers with other wavelength requirements, get in touch with DK Photonics.

Relative Terms In PON System

ODN (Optical Distribution Network)

ODN is a FTTH fiber optic cable network based on PON equipment. Its role is to provide optical transmission channel between the OLT and ONU. Accroding the function, ODN from the central office to the client can be divided into four parts: feeder fiber optic subsystems, cable wiring subsystem, home line of fiber optic subsystems and fiber terminal subsystems. The main components in ODN include optical fibers, optical connectors, optical splitters and corresponding equipments for installing them.

OLT (Optical line terminal)

OLT is a terminal equipment connected to the fiber backbone. It sends Ethernet data to the ONU, initiates and controls the ranging process, and records the ranging information. OLT allocates bandwidth to the ONU and controls the starting time and the transmission window size of the ONU transmission data.

ONU (Optical network unit)

ONU is a generic term denoting a device that terminates any one of the endpoints of a fiber to the premises network, implements a passive optical network (PON) protocol, and adapts PON PDUs to subscriber service interfaces. In some contexts, ONU implies a multiple subscriber device. Optical Network Terminal (ONT) is a special case of ONU that serves a single subscriber.

APON / BPON

APON (ATM PON) is the first PON system that achieved significant commercial deployment with an electrical layer built on Asynchronous Transfer Mode (ATM). BPON (Broadband PON) is the enhanced subsequence of APON, with the transmission speed up to 622Mb/s. At the same time, it added the dynamic bandwidth distribution, protection and other functions. APON/BPON systems typically have downstream capacity of 155 Mbps or 622 Mbps, with the latter now the most common.

GPON

GPON (Gigabit PON) is based on the TU-TG.984.x standard for the new generations of broadband passive optical access. Compared with the other PON standards, GPON provides the unprecedented high bandwidth downlink rate of up to 2.5 Gbit/s, the asymmetric features better adapt to the broadband data services market. It provides the QoS full business protection, at the same time carries ATM cells and (or) GEM frame, the good service level, the ability to support QoS assurance and service access. Carrying GEM frame, TDM traffic can be mapped to the GEM frame, 8kHz using a standard frame able to support TDM services. As a carrier-grade technology standards, GPON also provides access network level protection mechanism and full OAM functions. GPON is widely deployed in FTTH networks. It can develop into two directions which is 10 GPON and WDM-PON.

WDM-PON

WDM-PON uses wavelength division multiplexing technology to access to the passive optical network. It has four programs as following:

1. Each ONU is assigned with a pair of wavelength, for uplink and downlink transmission, thereby providing the OLT to each ONU fixed virtual point-to-point bidirectional connections.

2. ONU uses tunable lasers, according to the needs of the ONU to dynamically allocate the wavelength, and each ONU can be shared the wavelength, the network are reconfigurable.

3. Using colorless ONUs, the ONU are independent from the wavelength.

4. Using a combination of TDM and WDM technology, Composite PON (CPON). CPON uses WDM technology in the downstream, and TDMA technology in the upstream.

EPON / GEPON

EPON (Ethernet PON) is the rival activity to GPON which uses Ethernet packets instead of ATM cells. GEPON uses 1 gigabit per second upstream and downstream rates. It is a fast Ethernet over PONs which are point to multipoint to the premises (FTTP) or FTTH architecture in which single optical fiber is used to serve multiple premises or users. EPON is an emerging broadband access technology, through a single fiber-optic access system, to access the data, voice and video service, and it has a good economy.